****creak of opening coffin****
****shakes torpor from head****
****reads thread****


I would look at your Carthian book they talk about why cities get abandoned in their "setting up new experiments" section

And I would agree that the best thing for a modern game is that "Something blocked expansion until now"

Now that could be broken down into two main groups.
"Other Vampires" and "Non-Vampires"

lets start with the "Non Vampires":
The most obvious would be a hostile pack of werewolves or a Circle of Mages who dislike vampires for whatever reason. In either case they had the power to drive off/kill any vampire who set up in their territory and so the nearby Prince never got to expand into the area.
This has the advantage that Mages and Werewolves have their own business and the loss of the power centre may have otherwise nothing to do with vampires. A single VERY nasty spirit infestation may have weakened the main pack which when weakened fell to a couple local Pure tribes who couldn't care about the local vampires. Or the circle of wizards turned on each other and died/were scattered to the four winds. You could also get weirder. Cults, Major spirits, Changing Breeds families. . . any of these could also work. And they either self imploded or were killed by outside forces that are focused on that things nature not vampire nature.


And now for "Other Vampires": Lots of reason the city was basically abandoned.

The city's vampiries were interested in the occult and they made a mistake. Perhaps they were Ordo of the palantine rite and summoned a dark spirit to learn the nature of demons so they could compare their own beasts to it. Perhaps the circle was a little too good at blood sacrifice and woke some ancient evil. Either way...something went wrong. Perhaps a few fled in time, or perhaps not. Either way once their were no vampires the problem went away....or at least went quiet (who knows if the PC's cane awake it again)

A traveler came in and baited the local sheriff into consuming her soul and then all the deputies changed somehow and the next couple of months saw a rash of Amaranth...and the few "survivors" have taken to the highways looking for new homes. and looking at the Night Horror's books you might find other such ideas like the Ragmen. The idea that something can attack, hunt, mess with vampires is a theme in the horror stories fledglings tell each other when away from the shadows of their elders and betters....And sometimes the monsters that feed on monsters are real.

And sometimes the monster are one of their own. Perhaps the area was politically based around a single powerful elder (very possible in a small city) who after hitting BP 7 started hunting the other vampires (Vitae addiction and maybe Diab addiction pushing things harder) killing/driving off the other vampires before eventually starving into torpor (the Prince thinks....and well the party is "expendable" and gives you lots of rumour horror stories to have them face down. Maybe during this time, or instead of thickening blood driving the change, the elder in question looses themselves to the beast...which would give a different flavor but a similar outcome.

The political system there broke down into conflict. Vampiric tyrannies are all too common. Perhaps there was pushback and effectively a civil war. Or perhaps some group tried to exert too much control and the other vampires fled instead of comply. Eventually the social system didn't have enough members to support itself and the controlling group had problems (lost faith when no-one showed up in the congregation? no quorum to vote? etc) and either broke up of turned on each other in a last pathetic splash of blood. There is an example of this in the Carthian book if you want a breakdown of what I mean.

A blood vendetta spiraled out of control. Two powerful elders, or two covenants, or whatever started to fight. Open conflict. Ghouls and childer dying. They started to bring in allies. The town isn't that big but they pulled. Old favors get called, emotions run hot. Soon "staying out of it" isn't possible. If you aren't with us you are with them becomes the call each night. Vampires hate and fear this kind of thing...for good reason because once it starts it can be hard to stop....here nothing stops it. An eye for an eye, a life for a life...The death toll mounts. A few flee but most are drawn into the maelstrom of death and unleashed beasts. Eventually the victors are too damaged to hold the city. Perhaps the "victors" are a couple of ghouls who killed the last vampire after that vampire killed their master...or perhaps the last survivor was a low level member of one side who looked upon what had been made of their fair city once the last enemy had been slain and saw only ruin lost coterie mates (even lovers) and knew they couldn't stay with the memories of the lost and the war. And so cede the city to whomever would have it free of their trauma, namely the PC's

perhaps some "other" type of vampire that could never hold the town caused the problem. A rampant contagious run of Malkavia (most fled, some stayed and died, perhaps a couple are still hiding out) could do the trick. Or perhaps the Brood swept through. A couple nomadic packs hitting the town like a blitzkrieg and weakening the Masquerade so badly that no sane vampire would stay even if they had survived (and this "patching the masquerade could be part of the party's job too). And as for blitzkrieg.....Seven. Seven came, Seven killed, none survived, Seven vanished. I mean this is the kind of thing Seven was put in the game for IMO.
Even a single nasty traveling vampire could possibly disrupt the city if it was already under tension and suddenly the upper layers get blown away. Morris Spiegel is an example from one of the later books (I think one of the Night Horror books but not sure off the top of my head nor sure I got the name exactly right) who likes blowing up whole elysiums to get one of his targets from years ago....And The Unholy may also work for such a trick. In either case once the main leadership suddenly finds themselves brightening sunsets the lower ranks run/turn on each other, see the ghouls of the elders turn on the young, and in all have a really bad time leading to more ash piles or highway trips.

all just a few ideas on why the town is creepily abandoned in vampire terms in the modern nights.